"Identity theories" of consciousness generally assert that the physical basis of thought (brains, etc.) is identical with thought. For the more physicalist versions of identity theory there is nothing more to be said: what brains do can be labeled thought/consciousness and that is the end of the matter (pardon the pun). For other versions of identity theory, we may subscribe to a dual aspect theory of consciousness that asserts a difference in kind between consciousness and matter - but there is a necessary and clear one to one correspondence between thoughts and matter. Under this version, if we know all there is to know about the state of a given brain, we know at least in theory everything about the experience associated with that brain. (The connection between the two is the subject of the "psychophysical laws" that Chalmers and others have written about). There is a third type of identity theory, however, that asserts the existence of further facts about consciousness that cannot even in theory be known through an exhaustive examination of the matter of a given brain. (Maybe this shouldn't be considered an "identity theory" after all, but it's a closely related species to be sure). This version accepts that there is a necessary correspondence between matter and thought and changes to matter will result in changes to thought. But this version also asserts that even if we knew literally everything that could be known about a given brain we would still not know everything about its associated experience/consciousness/thoughts. My question, then, is what arguments do we have for this third view? Libet has proposed an experiment that would, if performed successfully, show that the brain's physical connections are not sufficient to explain experience; rather, for Libet, there is a "conscious mental field" that is a heretofore unidentified field that mediates consciousness, in addition to the physical connections of the brain. Libet's experiment remains unperformed. However, what I'm looking for is a little different: evidence/arguments for the further facts of consciousness, which could not be discovered even in theory by an exhaustive examination of matter.